This invention relates generally to pressure transducers and more particularly to such transducers using strain gauge technology for sensing pressure change to produce an electrical signal related to such change and employing electronics for processing and amplifying the signal.
Although the use of strain gauge technology for converting changes in fluid pressure to related electrical signals is known, there exists a need to provide transducers which are more easily manufacturable and which have improved reliability and optimum life expectancy. There is also a need to minimize the cost of producing the transducers so as to make it more economically feasible to use them in given applications and thus increase manufacturing volume with resulting savings in large volume manufacturing techniques.
In copending application Ser. No. 09/723,139, assigned to the assignee of the present invention, a pressure transducer using strain gauge technology is disclosed and claimed comprising a tubular port fitting having a fluid receiving opening at one end and a closed, integrally formed diaphragm at an opposite pedestal end, an angular orientation feature and a locking feature for locking receipt of a support member on the pedestal end. The support member has an apertured flat end wall received over the diaphragm portion, the aperture being in alignment with strain gauge sensor elements glass bonded to the diaphragm portion. A flexible circuit assembly having a first lobe section for mounting electronic components is bonded to the rigid, flat end surface of the support with an opening aligned with the aperture in the flat surface. A second lobe section of the flexible circuit assembly is positioned on a seating surface of a connector mounted on the support member, the connector mounting terminals with free distal ends extending into an electronics chamber in which the seating surface is disposed. The free distal ends are received through apertures in the second lobe section and soldered to respective circuit pads thereon. Wires are ultrasonically bonded both to the strain gauge sensor elements and to circuit pads on the bonded lobe section of the flexible circuit assembly and encapsulated by silicone gel.
In a first embodiment, a cup-shaped EMC shield is received in the electronics chamber over the first lobe section of the flexible circuit assembly, the shield provided with tabs which extend outwardly through openings in the connector""s sidewall beyond the outer periphery of the connector""s walls. An intermediate portion of the flexible circuit assembly extending between the lobe sections is bent into a generally U-shaped configuration with wall portions of the connector locking onto the support member. An hexagonal metal housing member is received over the body of the connector with the EMC shield tabs spring biased into electrical connection with the housing member and with the housing member applying a selected load on an O-ring placed in a circumferentially extending groove formed in the sidewall of the connector body, the housing being welded around its lower periphery to a support flange of the port fitting to form a fluid seal and to maintain the loading on the O-ring.
In a second embodiment made especially for miniaturization, the connector has an elongated portion mounting terminals having spaced apart circumferentially extending contact portions. A ground ring is mounted on an external surface of the connector and the housing is formed with radially extending tabs at one end which are biased into electrical engagement with the ground ring when the housing is welded to the port fitting.
It is an object of the invention to provide an environmentally sealed pressure transducer which is particularly conducive to ease of assembly with minimal chance of misalignment of components during assembly which could cause damage to sensitive components within the transducer. Another object of the invention is the provision of a transducer with optimized yield and life expectancy. Another object is the provision of a transducer having elongated free length terminals for use with selected welded connections to terminals of ancillary equipment and for means to prevent bending of such terminals during assembly, handling and shipping. Yet another object is the provision of an improved environmental seal including a seal particularly adapted for use in harsh environmental conditions. Still another object is the provision of a transducer having improved reliability of electrical connections between an EMC shield and a ground conductor.
Briefly described, the pressure transducer made in accordance with a preferred embodiment of the invention includes a vertical stack of components of the type disclosed in the above referenced copending application including a tubular port fitting having a diaphragm at a pedestal end with strain gauge sensor elements mounted on the diaphragm, a support member having an end wall formed with a sensor element receiving window formed in the end wall, the support member mounted on the tubular port fitting, an electrically insulative connector mounting terminals received over the support member forming an electronic chamber between the support member and the connector and with a flexible circuit assembly bent into a U-shaped configuration received in the electronic chamber. An EMC shield having terminal receiving apertures has an end wall disposed between the connector and the flexible circuit and is connected to the connector by spring tabs wedged against sidewalls of a slot in the connector. The shield is formed with first and second legs, the first legs having at their distal free ends a foot extending out of the plane of the respective first legs adapted to be biased into engagement with a ground conductor of the flexible circuit assembly. The second legs have a catch and an outwardly extending cam portion at their distal free ends for being cammed outwardly when pressed against the outer periphery of the support member until the catch is received in a window formed in the support member thereby interconnecting the connector/EMC shield sub-assembly and the support member with the first legs of the shield being in engagement with the ground conductor of the flexible circuit assembly. The interconnection of the second legs of the EMC shield and the support member facilitates the proper alignment of the vertical stack of components during the assembly process, i.e., until a later assembled O-ring applies a compressive force on the stack.
According to a feature of the above embodiment, the connector comprises first and second separate body portions with an O-ring received on the first portion and a loading washer disposed over the O-ring. The second connector portion has a central hub receivable in a cavity of the first portion with a plurality of terminals extending through the central hub and down through bosses of the first connector portion and through the apertures in the EMC shield. The second connector portion is ultrasonically welded to the first portion and has an end wall retaining the O-ring and washer with the end wall formed with cut-out portions about its outer periphery so that protrusions formed on a housing can pass through the cut-outs and apply a suitable load on the O-ring through the washer. The load on the washer is applied and maintained by attaching the housing to the tubular port fitting as by welding. The washer serves to evenly distribute forces on the O-ring and prevent localized over-compression in the O-ring.
In another embodiment, an EMC shield in the form of a ring is insert molded into the connector with the ring having an exposed upper, radially extending surface forming an O-ring seat. The connector is formed with downwardly extending legs formed with a catch receivable in respective windows formed in the support member for positive attachment thereto. A tubular housing member is formed with an annular flange at an end thereof which serves to apply a loading force to an O-ring disposed on the seat to provide an environmental seal as well as to maintain a compressive force on the stack of vertically aligned components.
According to a feature of this embodiment, terminals extending through the connector may be provided with an extended free length portion to facilitate welding to an ECU unit or the like. A shroud is provided with terminal receiving grooves or bores removably interconnected with the connector to protect the terminals and prevent bending of the terminals during assembly, handling and shipping.
In another embodiment, a transducer particularly adapted for use when exposed to harsh environments comprises a connector having an elongated tubular neck in which a well is formed. An insulative insert having lead receptacle bores formed therein is received in the well. The insert supports a resilient grommet retained in the well by a snap cap. The grommet is a generally cylindrical member having longitudinally extending through holes for wires extending from the receptacles, a center gland extending around the outer cylindrical periphery and a plurality of cylindrical protrusions extending downwardly from the bottom face to provide space relief and avoid over-compression. Wire leads connected to the terminals within the insulative insert provide orientation insensitivity.
Additional objects, features and methods of the invention will be set forth in part in the description which follows and in part will be obvious from the description. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations and methods particularly pointed out in the appended claims.